Manufacture of zinc oxide



Jan. 2, 1934. B, N. M C V 1,941,569

MANUFACTURE OF ZINC OXIDE Filed Feb. 24, 1930 2 Sheets-Sheet l INVENTOR BY (PM ci l ATTORNEYS Jan. 2, 1934. B. N. M CRAVEN MANUFACTURE OF ZINC OXIDE Filed Feb. 24. 1930 2 Sheets-Sheet 2 v INVENTOR BM /v. m 01 fiM- m ATTORNEYS Patented Jan. 2, 1934 MANUFACTURE OF zINc OXIDE Bonner N. McCraven, Bloomfield, N. J., assignor to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application February 24, 1930. Serial No. 430,839

5 Claims. 401. 23-148) This invention relates to the manufacture of zinc oxide, and has for its object the provisionof an improved method of making zinc oxide;

The invention is particularly applicable to the production of zinc oxide from zinc vapor derived directly from a reducing or smelting operation. The zinc vapor produced by 'a reducing or smelting operation is diluted with carbon monoxide gas and contaminated with sulfur originating usually in the carbonaceous reducing agent (such as coal Zinc'oxide resulting from the direct oxidation of such zinc vapor is accordingly con-f or coke) taminated with adsorbed sulfur compounds and directlyfrom ore by the so-called- American process and is inferior in quality to French process zinc oxide (made from zinc metal) largely on acclountof its'sulfur content. One of the principal aims of the presentinventionis to produce zinc oxide from areducing or smelting operation without contamin'ationwith sulfur' compounds. In accordance with the invention, the zinc vapor from the reducing or smeltingoperation is condensed in a condenser of appropriate capacity, whereby the carbon monoxide and sulfur gases are eliminated through the exhaust gas outlet of the condenser. The resultingmolten zinc metal is permitted to flow from the condenser into a volatilization chamber maintained iata.

sufiiciently high temperature to volatilize zinc and deliver the resulting zinc vapor to an, ap-. propriate oxidizing environment, andtheresulti ing zinc oxide is collected in any appropriate manner.

The invention in its broad aspect is applicable to the, production of zinc oxide from any source of zinc vapor. The zinc vapor is first condensed,

. oxidizing gas is admitted inappropriate volume.

These and other novel features of the invention.

will be best understood fromthe following deresembles "in quality the zinc, oxide produced scription taken in conjunction with the'accompanying drawings, inwhich Fig. 1 ma sectional elevationof an apparatus adapted for the practice of the invention;

Fig. 2 is a sectional elevation of the same apparatus on the section line 2-2 of Fig. 1; and Fig. 3 is a sectional'elevation of aslightly modifled volatilization chamber. 1

A vertical retort smelting operation is illustrated in the drawingsfas the source of the primary or initial zinc vapor. This smelting operation may advantageously be carried out as described in U. S. Patent'1,712,132.by progressively passing an agglomerated charge 6 of mixedzinciferous and carbonaceous materials through a. vertical retort 7 within the heating chamber or laboratory 8' of.an appropriate furnace structure 8. The upper end of the vertical retort 7 communicates with a down-draftcondenser con-f sisting ofa baffled condensing chamber 9 and a communicating bafiied condensingand collecting sump 10, generally of the tYPfideScribe'd in the copending patent application of ,EarlH. Bunce, Serial No'. 400,064, filed October 16,1929. The sump 10 has av chimney or stack ll for the exhaust of gases, other than zinc vapor entering the condenserf v v f The'bottom' of the sump 10 is inclinedlengthwise from eachlend'and is provided on one side with a'tap hole ,12 at the apex of the inclined" bottom surfaces; On theother sidegattheyapex of its inclined bottom sui faces,. the fsump is'connected by a conduit 13 witha volatiliz'ation cham-r ber or fretort 14 appropriately. mounted) within a furnace structure .15.: The conduit '13 is surrounded by a heating laboratory 16 in communication with the heating laboratory 15'. surround mg the chamber. 14, and the exhaust" heating a common stack or chimney. 17. V

1 The volatilization chamber 14 is closed at its top except for a vapor dischargenozzle 18. The nozzle 18 is surrounded by a wind box 19 adapted to direct an annular blast of oxidizing gas (such as air) against the stream of zinc vapor issuing through the nozzle, as more particularly described in U. S. Patent 1,522,097. Compressed air is supplied to the wind box by a pipe 20 communicating with a valved cold air supply pipe 21 and a valved hot air supply pipe 22. A hood 23 is mounted above the volatilization chamber and constitutes an enclosed oxidizing environment for the zinc vapor issuing through the nozzle 18. The hood is connected by an off-take pipe 24-to a bag-room or other zinc oxide collecting means (not shown).

gases from the two laboratories are conveyed to Clean oxidizing gas is supplied to the interior of the hood 23 through a pipe 25, and a fan or other appropriate suction means is associated with the off-take pipe 24 to induce the desired suction or draftwithin the oxidizing environment provided by the hood 23. W s

A pair of hollow graphite resistors 26 extend through the top of the chamber; 14 into the bath of molten metal in the chamber.

are provided (for an appropriate length) with spiral convolutions, as more particularly described in U. S. Patent 1,674,947. The resistors are c on- ,nected to an appropriate source of electric energy.

In Fig. 3 of the drawings, the volatilization" chamber 14 and conduit 13 are surrounded with a relatively thick layer of heat insulating material, in order to dispense with theheatinglaboratories illustrated in Fig. 2.

of the volatilizing chamber. W

In practicing the'invention illustrated in the dravs rings, the'zinc vapor from The condensed molten zinc collecting in thesump 10 ,flows'through the conduit 13 into the volatiliz ing' chambenl so that the leyel of molten metal (a) is the samein both the sump 10 and chamber 14. Hot gas'esat a temperature otjro'm' 90o} 1000" C. (preferably the exhaust heating] gases 7 ,fromthe reducing Iurnace'm enter the heating} aroundthe'chamber 14 andconduit 1; a assist in'heating'the molten zincin the chamber. The

further heat] required fer volatilizingl zinc at e uet ve city s nl s d' h sit i 40 in the volatilization chamber.

Th ran e en P52 e e ed .r st 16T makes it possible todetermine at given time the exactlevel m) of molten zincin the condens ing' sump 1Q and tojegulate this level with precision'. Since the sump locommun'icates freely with the chamber14 through the conduit 13 the vel nmolt ncin b t ump. n sh m.-

b 1 always the same. as thedepth or me bat 1i of j'molten zinc in thechamber 14 increases, the. istor .6..b more d p y mer in me olten met dth efiect v g v o the res s I torsis shortenedsothat an increas'ed electric" current flows through the resistors and more heat metal in the chamber 14 falls, theeifective length of the resistors is increased, thus" increasing the electric resistance and decreasing the current the level of molten zinc in both the sump and the- V volatilization chamber. 7 v i If too much molten zinc builds ;up .in the sump 10, so that the automatically increased supply of heat from the resistors 26 cannot compensate for the increase by volatilizing more zinc from the chamber 14, molten zinc may be tapped from til the sump through the tapping hole '12 or a tap The. resistors pr; zincvapor issues from the nozzle it encounters The resistors 26 are ,oxidjzedto zinc oxide. positioned outside the hood 23 and near'one end and condensing sump 10., The carbon monoxide sistoifs 26 which dipinto'the bathof molten 'zinc' "iseVolved, and the quantityljoi zinc volatilized is accordinglyuncreased'." As the level of molten withinlthejhoo.

5 flow, so that less heat is supplied to the bathof temperature to volatilize zinc and deliver the resulting zinc vapor through the nozzle 18 in a substantially;continuous stream. As the stream the annularblast of oxidizing gas from the Wind box, 19, the. zinc is immediately burnt or The suspended particles of zinc oxide are drawn through the off-take pipe 4 int the oxide-collecting system Z111 ide P duces-m? some" inventionzisgof high Qdllfility Comparable grade French. processi'oxide, and is, dev

ie -5mm ui zl a di 'l i were the pipe; 22 can be mixed, in any 1 desired p.170

is' efle'ct'ed'by the'air inlet 1 e2'5" which co clean air taken irom, apoint at a distanceirqni any source or soot'ordust, a d,preie ab'lyicleau d its by air. filters into the oxidizing environment heginv, til practiced thejapparat] r th dmi ns da, d for thlep en Z 'i e s- 11 o d .of mi e-1B5 sired particle size W] houta'ny substan am; iust 'h nt n, Passing, iromjone operation ,mmeer A Q a rpartof .t vap r derived; fr m. he .s'm ine..1 u naecan "be ecorered a I either rzincfpo'xide' drains-metal. 'Ifheyol msh rosin-em maintaining proper operat i I condenser .01? the smeltin peratic ence. of,.a.controll e'd amount ormeu v condenserlis necessary i611 .Dntimfim. ,oo de conditions; -Tne volaniizati a plumper both. as means f iloinaticallyieeula hedepth O lt imetal in, the condenser ahdlas'. an, ndicator. of the amountjlo amen ,metal' actuallypre'sent' in the condensing sump, thus I cording to claim 1, which comprises effecting the in the liberation of zinc vapor and the evolution of gases, condensing the zinc vapor to a bath of molten zinc while permitting the gases to escape from the system, continuously flowing molten zinc from said bath of molten zinc by gravity while substantially conserving its heat and unaccompanied by gases and not in contact with air into a second bath of molten zinc excluded from contact with said gases, volatilizing the said second bath of molten zinc excluded from contact with gases to zinc vapor, and burning the resulting zinc vapor to zinc oxide.

2. A method of manufacturing zinc oxide according to the preceding claim, which comprises utilizing the exhaust heat of the reduction. operation to supply heat to the molten zinc volatilization operation. t

3. A method of manufacturing, zinc oxide according to claim 1, which comprises maintaining the second bath of molten zinc substantially constant in volume by volatilizing zinc therefrom at substantially the same rate as zinc vapor is condensed in the first bath of molten zinc.

4. A method of manufacturing zinc oxide acvolatilization of the second bath of molten zinc by heat supplied by resistance electrodes dipping into the bath of molten zinc so that a circuit is completed through the bath of molten zinc, whereby an increase in the depth of thebath of molten zinc shortens the length of resistor to be traversed by electric current, then increasing the flow of current and the supply of heat so as to increase the amount of zinc volatilized, and

whereby a decrease in the depth of the bath of molten zinc extends the length of resistor to be traversed by the electric current, thus increasing the flow of current andthe supply of heat so as to decrease the amount of 'zinc volatilized,, whereby the depth of the first and second baths 5. A method of fmanufacturingzinc oxide,

which comprises reducing zinciferous material to produce zinc vapor, maintaining by the con- 'densation of said zinc vapor a molten bath of zinc metal in full communication by gravity with a second molten bath of zinc metal from which BONNER, N. MCCRAVEN. 

